PROCEEDINGS 



OF THE 



GEOLOGICAL & POLYTECHNIC SOCIETY 



AT THE THIRTT-SECOND QUARTERLY MEETING, HELD IN THE 

 CONCERT ROOM, YORK, 

 ON THURSDAY, THE 23RD JULY, 1846. 



The Right Hon. the Earl Fitzwilliam, F.R.S., President, 

 in the Chair. 



The Noble Chairman stated that Dr. Lyon Playfair 

 was to have read a paper at this meeting on " The Chemical 

 Effects of Summer Fallows," but having lately taken unto 

 himself a partner, he was not able to attend on the present 

 occasion. He (the Chairman) should, therefore, call upon 

 the Rev. Dr. Scoresby to read his paper 



ON THE construction AND PERFORMANCES OF THE EARL 

 OF ROSSE's gigantic TELESCOPE. 



The Rev. Dr. Scoresby, after a few introductory observa- 

 tions, remarked that he might have occasion to refer very 

 briefly to the principle of the instrument as necessary to the 

 Illustration of his subject. For the information of those who 

 might not be aware of the construction of the telescope, he 

 would observe that the principle upon which it acted was this, 

 — it simply depended upon the property of a convex glass and 

 of concave reflectors, which produce an image at their focus. 

 For instance, if he had a magnifying glass, and admitted the 

 light through that, more particularly in the way of the camera 



